While the state of Virtual/Mixed/Augmented Reality (XR) is constantly in flux and improving all the time, Unity have announced with Unity 2019.3 that their built-in XR support is being deprecated.
Unity 2019.3 is the next upcoming (Edit: now out after we published this) major build of the Unity game engine, currently in Beta and when released they're going to be pushing their newer unified XR plugin framework. It makes sense, giving developers of XR hardware the chance to get updates out a lot quicker, rather than waiting for engine upgrades.
With this change, Unity developed official XR plugins for "supported platforms" including ARKit, ARCore, Microsoft HoloLens, Magic Leap, Oculus, Windows Mixed Reality and PlayStation VR. Notice anyone missing? Valve. That's because Valve are developing their own OpenVR Unity XR plugin in-house. Hopefully this process will enable Valve to improve SteamVR support in Unity for Linux, since they will control the plugin.
Unity 2019.3 is also the first version of Unity that will properly support IL2CPP on Linux which the lack-of has caused issues for some developers.
You can read more about Unity's plans for XR on their blog post.